1. Field of the Invention
The invention is directed to a process and apparatus for the volume reduction of radioactive liquid waste solutions, particularly evaporator waste bottoms containing, for example, either boric acid or sodium sulfate and trace quantities of activity.
2. Description of the Prior Art
Pressurized Water Reactor (PWR) liquid waste streams potentially contaminated by radioactivity are treated in evaporators for the volume reduction of the waste and the reclamation of a clean condensate. The condensates from these evaporators are monitored and recycled after a polishing/demineralization treatment. The evaporator process affords an approximately fifteen to twenty fold volume reduction of the contaminated wastes. Although this is a significant volume reduction, there still remains a substantial quantity of waste evaporator bottoms which must be disposed of.
U.S. Pat. No. 4,119,560 discloses a process of waste volume reduction in which a solution of a liquid solvent and a solid solute is introduced into a hot inert carrier under highly turbulent conditions and at a temperature sufficient to cause the solvent to flash leaving dried dispersed solid particles. In this process, it is then necessary to separate the solid particles from the carrier. Another example of waste treatment is disclosed in U.S. Pat. No. 3,507,801 in which a mixture of radioactive waste water and a sodium borate solution is thickened by heating until the remaining quantity of water is small enough to be bondable by the sodium borate as water of crystallization. The apparatus utilized in such a process can experience scaling and corrosion.
After being subjected to a volume reduction process, the evaporator bottoms are packaged for final disposal. Current disposal methods primarily utilize the technique of mixing or absorbing the waste evaporator bottoms with cement, cement-vermiculite or solidifying with urea-formaldehyde and modified water-extendable polyesters in 55 gallon drums. The packaging method must overcome the problems of leaching and possible escape into the disposal environment.
Both the substantial rate of waste production and the potential regulatory restrictions for current disposal methods have pointed to the need for effective methods of waste volume reduction, packaging and disposal. The present invention is directed to a process and apparatus for the efficient volume reduction of liquid waste containing boric acid or sodium sulfate. Because the product rendered by the instant process is in a solid-liquid slurry form, the waste can be readily mixed with a packaging agent such as cement. As a result, the difficulties previously encountered with leaching are significantly reduced, if not totally eliminated.
It is an object of this invention to provide a process and an apparatus for the volume reduction of low level nuclear waste that precludes waste buildup or wear on mechanical components and that minimizes surface fouling caused by crystal growth.
Another object of this invention is to eliminate crystallizer fouling or freeze-up encountered in other volume reduction systems. The present volume reduction process can operate at an ambient temperature with a low turbulence liquid waste flow.
It is still another object to provide a reduced volume output in a solid-liquid slurry form in which the generation of radioactive dust is eliminated.
These and other objects of the invention will be readily apparent from the description with reference to the accompanying drawings.